President Obama speaks on the phone with King Abdullah II of Jordan in the Oval Office of the White House on Aug. 8. / Brendan Smialowski, AFP/Getty Images

by Jim Michaels, USA TODAY

by Jim Michaels, USA TODAY

WASHINGTON - In authorizing targeted air strikes against Islamic militants in Iraq, President Obama has opted to avoid the all-out "shock and awe" campaigns of previous U.S. conflicts in Iraq.

Air strikes will be limited to defending American forces and supporting a humanitarian effort to provide food and water to thousands of starving Yazidi refugees who have fled Islamic State militants because they practice a different religion.

On Saturday U.S. fighters and drones launched attacks that destroyed militant armored personnel carriers and an armed truck near Sinjar, according to U.S. Central Command.

The U.S. military said the strikes were conducted to protect civilians who were being fired on by the militants.

That response may prove inadequate to force the retreat of a surprisingly ferocious enemy that has evolved into a conventional army equipped with tanks and heavy weapons. Many of those weapons, including Humvees and artillery, are American-made and were seized from Iraqi national troops who fled Mosul, Iraq's second-largest city, when the militants attacked in June.

The air strikes will be limited in scope and not part of "a larger air campaign at this point," a senior defense official said Friday. He asked not to be named because he was not authorized to talk publicly about the decision.

However, if militants attempt to pursue the refugees, who have fled to a barren mountain, interfere with resupply efforts or threaten the nearby city of Irbil, the bombing could be more sustained, the official said. Irbil is the capital of the semi-autonomous Kurdish region in northern Iraq and home to a U.S. consulate and U.S.-Iraqi joint military operations center.

"ISIL has a vote in how sustained this is," the official said, referring to Islamic State of Iraq and the Levant, the full name of the militant group.

The type of air attacks authorized by Obama contrast with bombing campaigns in Iraq in 1991 and 2003 when U.S. war planes and ships firing cruise missiles unleashed massive bombings in an attempt to break the back of Iraqi dictator Saddam Hussein's military apparatus from the outset to aid allied ground attacks that would soon follow.

The current air campaign "will be defensive and it will be somewhat limited," predicted James Jeffrey, a former U.S. ambassador to Iraq.

Jeffrey and other analysts warn that U.S. military involvement might be forced to widen, however, because the Islamic State poses such a significant threat to Iraq's sovereignty. Only a more robust military response can halt Islamic State's unrelenting progress across Iraq, Jeffrey said.

The Pentagon will need to intensify its air strikes and put advisers in Iraq to stop the progress of the Islamic State, which has yet to suffer a significant setback at the hands of Iraqi security forces, he said. "That is going to require air power along with competent folks on the ground."

So far, President Obama has resisted such broader moves three years after ending U.S. combat in Iraq.

The Islamic State is not a ragtag force of militants, but rather a conventional army equipped with tanks and other heavy weapons and equipment, according to analysts and the Pentagon. The first American air strike was aimed at a mobile artillery site threatening Irbil, according to the Pentagon.

The militants have gained critical combat experience fighting alongside opposition groups that have waged a civil war against Syria's military for three years.

Plus, they are well financed. The group receives funding from donors in wealthy Persian Gulf states and the militants have seized critical infrastructure in areas they control. Currently they are attempting to seize massive hyrdroelectric dams in Mosul and Haditha that provide much of Baghdad's electricity. They have seized oil fields in Syria and Iraq.

"They are flush with resources, cash and equipment," Brett McGurk, a State Department official, testified recently.

They have also teamed up with former Iraqi army officers who bring experience in tactics and the employment of heavy weapons. The officers are Sunnis who have been alienated by Iraq's Shiite-dominated government.

"ISIL is no longer simply a terrorist organization," McGurk said. "It is now a full-blown army."

They have been unstoppable in recent months, leaving in their wake destruction and thousands of refugees. Typically these radical Sunni Muslims drive out all other religious groups once they seize an area, including Shiites, who are a majority in Iraq, Christians and the Yazidis who are now the focus of U.S. aid.

The Pentagon estimates the militants now control about a third of Iraq's territory.

Little stands in their way. Four Iraqi divisions collapsed when the militants attacked Mosul. Most of the remaining Iraqi forces have since been redeployed to defend Baghdad.

With every victory the Islamic State gets stronger and "our allies get weaker on the ground," Jeffrey said.